Patent FR-2,501,777 mentions a known method and device for carrying out measurings and/or servicings from a sonde fastened to the end of a drill string, but this document only relates to logging devices and has no intermediate connectors. The rotating of the whole of the string in the well is impossible when the sonde is connected because of the presence of the cable coaxial with respect to the drill string or annular when a side-entry sub is used.
The present invention allows to connect measuring and/or servicing means notably included in a drilling assembly and allows the rotating of the whole of the string without requiring the total coaxial cable to be taken up to the surface, by means of intermediate connectors and of an adapted support.
Document GB-1,557,863 mentions a known method and device for transmitting information coming from a sonde lowered in a drill string, said sonde being suspended to a cable section, said section being linked to the surface by means of a connector and of a cable. The sonde is lowered into the string at the end of the cable and must therefore have an outside diameter compatible with the inner passage of the tubular string, and the hanging of the section is achieved at the surface.
The present invention advantageously allows a size of measuring devices which no longer depends on the inside diameter of the drill string channel. In fact, in small drilling sizes, it is sometimes impossible to have certain equipments. The invention integrates the measuring and/or servicing means in housings which may have the outside dimension of the drill collars conventionally used in the borehole considered. The electronic elements are linked to the surface by a device comprising at least one double couple of electric connectors. Operating the pipes so as to take them down or up can be easily done by taking up a limited cable length, which only requires a very short time and allows high capacity transmissions by means of a cable transmission. No cable in the annulus, as it is commonly the case in this field when a side-entry sub is utilized, is advantageous when safety imposes an annular seal at the well-head, either continuously in case of air drilling or foam drilling, or occasionally when the bottomhole pressure is unbalanced. In these cases, the cable is bothersome and sometimes dangerous.
In certain strongly deflected wellbores, notably those with a small bending radius, this invention is economically very interesting for the phase of control of the trajectory of the wellbore in the curve and in the substantially horizontal part. In fact, the tools used in the prior art use notably a transmission by pressure waves in the fluid so as to be able to rotate the total string without the cable being in the way or having to be taken up completely. With the invention, the length of the section may correspond to the kick-off point, and since the length of the wellbore with a small bending radius is limited to several hundred meters, maneuvering the cable connected to the surface is simple and fast during the total deflection phase. With the invention, the frequency of the measurings and servicings is thus comparable to what can be obtained with transmissions without an electric cable, and moreover with a lesser cost and complexity. Moreover, rotating the total string is allowed when the cable has been taken up to the surface.
In the case of very deep and therefore very high temperature drilling, the invention will be advantageously applied because it provides a mechanical support for taking up the weight of the cable and the tensile strains generated on the cable notably through an energetic circulation of a cooling fluid. In fact, in deep drillings, the tension which a continuous cable would withstand is higher than the allowable tension. The solution therefore consists in having intermediate supports of sections with an acceptable length.